I deleted a friend and then added him/her again, but now I cannot see him/her in the list. Why?

If you add a new friend or add back a friend whom you have mistakenly deleted, you will have to wait for approximately ten minutes until your frindlist and the online status of your friends are updated. After this time the new friend will appear in your list, you will be able to send him gifts, visit him and invite him to battles.